The present invention relates to message transfer between digital data processing stations interconnected by a communications network. More particularly, the invention discloses a method for simultaneous message transfer between the station processor and the station interface component.
Dramatic growth in the use of microprocessor based devices has led to communications networks allowing for the interconnection of many of such devices to facilitate communication between the devices. A typical network, such as a local area network (LAN), includes a number of microprocessor devices or stations which are interconnected by a number of communication channels or links. Some of the devices or xe2x80x9cstationsxe2x80x9d may be xe2x80x9chalf-duplexxe2x80x9d stations meaning that they are capable of transmitting and receiving data, but cannot transmit and receive data simultaneously. Other stations are xe2x80x9cfull-duplexxe2x80x9d stations which are capable of transmitting and receiving data at any given time or simultaneously transmitting and receiving data.
Typically, communication between stations interconnected by a network is accomplished through a peripheral communication device. This device acts as an interface between the host microprocessor of the station and the larger communications network. Depending on the network protocol, the data communicated on this network often takes the form of a message. The peripheral device, acting as a communication interface, must be capable of receiving and storing message data for the station from the network, and transmitting message data from the station onto the network. All information transmitted and received on the network must conform to a preestablished protocol. Messages are transmitted in frames of uniform format, each frame comprising a number of fields each having a predefined location and meaning.
The interface between the station microprocessor and the peripheral communication device is often implemented using a serial peripheral interface (SPI). The SPI typically uses four connections between the microprocessor and the peripheral communication device to accomplish the transmission and reception of network message data. While this arrangement is generally satisfactory, the efficiency of such an arrangement is compromised due to the excessive amount of time spent by the station microprocessor servicing the SPI. Accordingly, it will be appreciated that it would be highly desirable to provide a method which allows for efficient full duplex communications between stations on the network by simplifying message transfer between the station microprocessor and the SPI.
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a method for more efficient full duplex communication between stations on a communication network is provided. The method allows for simultaneous initiation of network message transmission from the station microprocessor to the peripheral device while reading a stored received network message transmission from the peripheral device to the microprocessor in a single serial transfer. The method has particular application to several scenarios which typically occur during message transfer between stations on the network.
The present invention provides efficient full duplex communications between stations on the network. It provides a method which allows for simultaneous initiation of network message transmission from the station microprocessor to the peripheral device while reading a stored received network message transmission from the peripheral device to the microprocessor in a single serial transfer. It provides a network communication method which reduces the amount of time spent servicing the peripheral device by the station microprocessor. This method is particularly applicable for four commonly encountered scenarios. The first scenario occurs when a transaction, i.e., an outgoing message intended for other stations on the network, is initiated by a station microprocessor with a network received message stored in the peripheral device. The second scenario occurs when a transaction is initiated by a station microprocessor without a network received message stored in the peripheral device. The third scenario occurs when a dummy message transmission is initiated by the host processor and a network received message is stored in the peripheral device, and the fourth scenario occurs when a dummy transmission is initiated by the host processor and a network received message is not stored in the peripheral device.
The message protocol associated with the method supplants any existing SPI protocol. The message format is byte oriented, with the first byte of the microprocessor message containing command signals and the remaining bytes containing transmission data or dummy data. The byte oriented message stored in the peripheral device, which has been received from the network, includes a first byte containing a status signal with the remaining bytes containing received data or dummy data. The message received from the network is translated from the network protocol to the message protocol used for exchanging messages between the peripheral device and the microprocessor. Dummy data is periodically transmitted by the microprocessor in order to check the status of the peripheral device and to retrieve any data stored therein. Likewise, if a transmission is initiated by the microprocessor and there is no received data stored in the peripheral device, dummy data is sent to the microprocessor.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.